Ground trainer for simulating the engines and propeller vibrations of multiengined airplanes



2,486,488 PEQLER 'Nom E, i949. J. J. LUKACS GROUND TRAINER Foa sIM ULATING THE ENGINES AND PRO VIBRATIONS OF MULTIENGINED AIRPLANES Filed March 20, 1946 A TORNEY Patented Nov. 1, 1949 GRUND TRAINER FOR SIMULATING THE ENGINES AND PROPELLER VIBRATIONS OF MULTI'ENGINED AIRPLANES loseph .1'. Lukacs, New Rochelle, N. Y., assignor to Bell |Telephone Laboratories, Incorporated, New York, N. Y., a cor-poration of New York Application March 20, 1946, Serial N0. 655,790

7 Claims.

'This invention relates to a ground trainer for training aircraft crews and more particularly to circuits and apparatus for simulating the engine and propeller vibrations of a multiengined airplane.

Engine and propeller vibrations have heretofore been simulated 'in an aircraft trainer but such simulation has not been as realistic as desirable when applied to a trainer intended to simulate a multienglned airplane because no provision has been made for changing the intensity of the vvibrations as a result of the engines running at different speeds.

It is the object of the present invention to more realistically simulate the vibrations produced in a multiengined airplane due to the operation of the engines at unequal speeds.

In accordance with the invention which has been disclosed as applicable to a trainer for simulating'a four-engine airplane, two vibrators are provided, one mounted at the forward end of the flight deck and the other mounted at the aft end of the flight deck. Each vibrator comprises an eccentrically mounted weight rotatable by a motor.

The motor of the forward vibrator is controlled by either one of two variacs or variable transformers, one of which is a part of the R. P. M. motor unit which simulates one of the in-board engines of an airplane and the other of which is part of the R. P. M. motor unit which simulates the other of the in-board engines. A relay is provided for switching the vibrator motor to the control of either lone of the variacs. Similarly the motor or the aft vibrator may be switched by a second relay to the control of either one of two other variacs associated respectively with the R. P. M. motor units which simulate the outboard engines of an airplane.

Control of the forward vibrator by the associated relay is taken over by the simulated inboard engine which has the greater simulated R. P. M. and control of the aft vibrator by the associated relay is also taken over by the outboard engine which has the greater R, P. M. To accomplish this two comparison circuits are provided, one of which continuously compares signal potentials derived by two potentiometers associated respectively with the R. P. M. motor units which simulate the in-board engines and the other of which continuously compares signal potentials derived by two potentiometers associated respectively with the R. P. M. motor units which simulate the out-board engines. The first of these comparison circuits controls the switching relay to control the switching of the forward vibrator motor to the variac of the R. P. M. motor unit of the irl-board engine which has the larger simulated P. M. and the second of the comparis-cn circuits controls the switching of the ait vibrator motor to the variac of the R. P. M motor unit of the out-board engine which has the larger simulated R. P. M.

Each comparison circuit comprises an input transformer, a single stage of amplification, a bias rectifier, a thyratron tube and a relay. Potentials of the same phase are applied to the primary winding terminals of the transformer from potentiometers of two R. P. M. units which simulate the two engines whose speeds are to be compared. If the potential on the upper terminal is greater than the potential on the lower terminal, the difference of potential is impressed on the secondary winding of the input transformer, is amplied and then impressed on the control grid of the thyratron tube as a potential of the phase pl causing that tube, which will have a potential of the same phase applied to its anode, to fire and operate the relay connected int-o its cathode-anode circuit. If, however, the potential on the lower terminal of the primary winding of the input transformer is greater than the potential on the upper terminal of the primary winding, the resultant amplified potential on the grid of the thryratron tube will be of phase e2 or opposite to the phase pl potential applied to the anode of the thyratron tube and such tube will not lire to operate the associated relay. The relay, when operated, causes the operation of the associated switching relay.

While the invention has been disclosed as applied to a trainer which simulates an airplane having four engines, it is to be understood that it is equally applicable to trainers which simulate two engined airplanes in which Case but one vibrator and one comparison circuit would be required. lt will also be apparent that another type of vibrator might be controlled to simulate the engine and propeller vibrations.

The invention having been briefly described, reference may now be had to the following detailed description read in connection with the accompanying single sheet of drawings which discloses the forward and aft vibrators, the two comparison circuits and the schematic representation oi such portions of the R. P. M. motor units which are operated to simulate the speeds of rotation of the four engines of an airplane.

Each of the motor units disclosed schematically in the dot-dash boxes in the right portion of 3 the drawing, is of the general type disclosed in Patent No. 2,428,767, granted October 1li, 1947, to W. H. T. Holden, R. H. Gurnley, R. C. Davis and W. P. Albert and in the application of J. J.

Lukacs and W. B. S'trickler, Serial No. 542,8l6, led June 30, 1944. Such a motor unit comprises a motor, such as motor l, which through a reduction gear box 2 drives a shaft 3. The shaft 3 through pairs of gears, such as 4 and 5, drives a plurality of potentiometers, such as R. P. M. H1, and variacs, such as VIB 1, which enter into the control of various circuits of the trainer. The motor l may be driven in one or the other direction under the control of a motor control circuit whereby the shaft 3 and the sliders of the potentiometers and variacs driven therefrom are rotated into positions commensurate with the assumed R. P. M. of the engine which the motor unit simulates. The motor control circuit may be controlled in a manner similar to that described in the aforementioned application. As indicated by the labels applied to the several boxes, the motor unit disclosed in boxes 6 and 'i simulate respectively the Nos. 1 and 4 out-board engines and the motor units disclosed in boxes 8 and 9 simulate respectively the Nos. 2 and 3 inboard engines. To simplify the drawing, the motor, reduction gear box, driving shaft and gearing have been omitted from boxes S, 1 and 9.

Each motor unit is also provided with a cam operated switch V which is held in its open position by a cam lll secured to the driving shaft of the variac VIB l until the slider of the variac has been moved to a position representative of an engine speed greater than approximately 350 R. P. M.

The potentiometer R. P. M. lll or" each motor unit has its winding shunted by a resistor il and is energized by potential applied across its terminals through a resistor l2 from a source of alternating current which may, for example b-e of 60 cycles at 40 volts and of phase e2. As soon as a simulated engine speed in excess of 350 R. P. M. has been attained by a simulated engine and the switch V oi the motor unit which simulates such engine becomes closed, alternating current is applied from a power source across the terminals of the variac VIB l whereupon a potential is derived from the slider of such variac. functioning as an auto transformer, for application to one of the vibrator motors. For example, if the switching relay 2-3 is unoperated, power is applied from the slider of the varias VIB 'i of the motor unit 3 for simulating the No. 2 engine, over the back contact of relay 2-S, through the choke coil i3 through the fle-ld winding and armature circuit of the forward vibrator motor FVM and thence through choke coil lil to the ground terminal of the source of power. It, however, relay 2 3 is operated, indicative of the fact that the simulated speed of the No. 3 engine is greater than the simulated speed of the No. 2 engine, power is applied from the slider of the variac VIB 1 of the motor unit 9 for simulating the No. 3 engine, over the front contact of relay 2 3. thence as traced through the motor FVM to the ground terminal of the source of power. Similar circuits through the motor AVM and over either the back or front contacts of relay l-IS and to the sliders of the variacs associated with the motor units 6 and 'l may be traced.

The vibrator motor unit comprising the motor FVM and eccentrically mounted weight 55 driven thereby is mounted on a forward bulkhead of the trainer and the vibrator motor unit compris- 4 ing the motor AVM and eccentrically mounted weight 56 driven thereby is mounted on an aft bulkhead of the trainer.

The two comparison circuits shown in the lower portion of the drawing are identical in structure. The No. 1 comparison circuit, for example, which compares the signal potentials derived at the sliders of the potentiometers R. P. M. I of the R. P. M. motor units 8 and 9, has an input transformer I5, the upper terminal of the primary winding of which is connected to the slider i6 of the R. P. M. lo potentiometer of motor unit 9 and the lower terminal of the primary winding of which is connected to the slider Il of the R. P. M. l!! potentiometer of motor unit 8. Since the potentials at the sliders Iii and l1 are measures of the simulated speeds of the Nos. 2 and 3 engines and are of the same phase fp2, the difference in potential between the terminals of the primary winding of transformer i is a measure of the diiference between the simulated engine speeds.

This difference potential is impressed upon the secondary winding of the transformer I5 and across the rheostat i8 from the slider of which potential is impressed through resistor I9 upon the control grid of the left unit of the amplifier tube 20. The left unit of tube is supplied with anode potential from the +130-Volt direct current source 2l through resistors 22 and 23 to the anode of tube 2Q. The cathodes of the tube 2D are heated conductively from the tube filament which is energized from the secondary winding of the filament transformer 24, the primary winding of which is energized from a 115- volt source of alternating current.

The amplified output from the left unit of tube 20 is applied from the anode of such unit through the coupling condenser and resistor 2S to ground and potential is applied from the junction point between condenser 25 and resistor 25 through resistor 21, the bias adjusting rheostat 28 and resistor 29 to the control grid of the thyratron tube 3U. The right unit of tube 2i] is utilized to rectify potential derived from the filament heating supply circuit for application as a negative biasing potential to the control grid of tube 3U. For this purpose the grid and anode of such right unit are connected together and the rectifying path through the right unit of thc tube extends from the lower terminal of the secondary winding of transformer 24, over the cathode-anode path through the tube, through the winding of rheostat 28 and re-resistance 2l to the upper terminal of the secondary winding of transformer 24. Potential derived at the slider of rheostat 28 is then applied through resistor 29 to the control grid cf tube 30. The biasing circuit is arranged to shift the value of the biasing potential to prevent the possibility of causing tube 3G to intermittently fire and cause relay 3l to vibrate when the resultant diiference potential applied from the ampliier tube 2G to the grid of tube hovers about the threshhold value Jfor just operating the relay 3l. Since a slightly higher voltage is required to operate relay 3l than is required to hold it from releasing, the resistor 21 is included in the circuit through the rectifier unit of tube 2i) when relay 3l is unoperated whereupon the bias potential applied to the grid of tube 30 is increased and tube 30 will fire only in response to a larger signal potential than when relay 3| is operated and resistor 2l is short-circuited. When relay 3l is operated and resistor 21 is short-circuited, the negative bias applied to the. grid of tube '30 is-decreased and a smaller signal potential is then required to' maintain relay3| operated.

-Relay 3| is'connected'in a circuit extending from a 60-cycle 11B-volt phase pIsource of current through the lamp resistor 33, thence in parallel with resistor-S32 and the 'Wind-ingof relay 3| through choke coil? 34, over the anode-cathodepath' through tube 3D to the ground termi* nal-of the source of current. The cathode Lof the tube is conductively heated from the iilament which is heated by current applied thereto from the secondary Winding of transformer 2.4. Relay 3| in addition to Acontrolling the shunt. of `resistor 2'! also controls'theestablishment `of an obvious circuit for lrelayy 2.3.

-The No. 2ucomparisontcircuit isiden-tical lto the No. l comparison .circuit just described except that .the upper zand lower terminals of .the primary Winding. of its input transformer 35are connected respectivelyto the. sliders 36 and 31 ofthe R. P. M. .I potentiometers associated with the,v motor -units and y6 which simulate the Nos. 4 and l engines .and that the relay 5| of vsuch circuit controls the switching relay |-4.

It "will be assumed that the simulated engines are all' running at the same speed and that as a consequence the phase .p2 lpotentials applied from' the sliders |16 and I'I tothe terminals of the primary winding of transformer I5 are equal and the phase va2 potentials-.applied from the sliders 36and 31 `to the terminals-f the primary winding of transformer 35 `are also equal. No potentials will therefore 'be impressed from the secondary windings .of transformers I5 and 35 .upon the control grids of the .amplier tubes 20 and 40 and no .amplified `signal potential will be applied to the control grids of the thyratron tubes 33 and 50. Such latter tubes -will .not therefore fire and relays 3|, 5I, 2-.3 and I-4 will remain unoperated.

With relays23 and |'-4 unoperated, the forward vibrator motorv FVM is, as previously described, under the control of variac WB I associated with the R. P. M. motor unit Band such motor therefore runs at a speedcomm'ensurate with the simulated speed of the No. 2 engine. Also the aft motor AVM is, as previously `described, under the control of Variac VIB 'I associated with the R. P. M. vmotor unit-9 and such motor therefore runs at a speed commensurate with the simulated speed of the No. l engine.

It will now .be assumed that a `reduction inthe speed of the No. 2 engine is simulated either by a closing of the engine throttle or by an engine failure sim'ulated under the control of the instructor. Asa result, the vslider of potentiometer R. P. M. Iiof .motor unit 8, through the operation of motor I, is moved back toward the No. 1 terminal of its winding thereby reducing the phase e2 potential applied to the lower terminal of the-primary winding of input transformer I5. The phase @2 potentials applied to the -terminalsof the primary winding of transformer I5 being now unequal, the difference potential impressed from the secondary winding of transformer I5 upon the grid of amplifier tube 20, ampliiied by such tube appears as a phase (pl potential on the control grid of tube 30 and since as previously described, phase pI potential is applied to the anode of tube 30, tube 30 will re each time the anode potential becomes positive and Will cause relay 3| to operate. The provision of choke coil 34 in the anode circuit of tube 30 insures that relay 3| will remain continuously operated so long as the signal'potentialiapplied. to thecontrol grid of tube 30 remains suiiiciently greatto cause tube .30 to re.

Relay 3| upon operating controls the normal negative bias Aofrelay 30 as previously described andv causes lthe operation of switching -relay 2-3 to switch controlof the forward lvibrator motor FVM from :the controlfof the vR. P. M. motor unit 8 of the No. 2 engine to the R. P. motor unit 9 Aof the No. 3engine which is now assumedto be operating at a higher simulated speed than the No.l 2 engine.

IIt will now be assumed that the simulated speed of the No. 2 engine is raised until it is greater than the 4simulated speed of the No. 3 engine. As a consequence, .the phase p2 potential applied fromrtne slider I1 is first raised through the movement of slider |'1 towards the No. 3 terminal ofthe potentiometer Winding until the potentials applied from' the sliders I6 and to the lower and upper terminals of the primary winding of transformer I5 again become equal and no ampliiied signal potential becomes applied to the control grid of tube 30. Hence with relay 3| at the time operated, the resistor 2`| is shunted over the lower contacts of relay 3| and vthe normal negative bias applied to the grid of tube 30 is therefore increased. Tube 30 will cease firing as the value lof the amplified signal is reduced toward a zero value and relay 3| will release in turn releasing relay.2-3. The control of the forward vibrator motor FVM is now returned to the control'of the R. P. M. motor unit which simulates the speed of theNo 2 engine.

.Asthe simulated speed of the No. 2 engine becomes further increased so that it is greater than the simulated speed of the No. 3 engine, the phase p2 potential Vapplied from the slider I1 to the lower terminal of the primary winding of transformer I5 becomes :greater than the phase p2 potential applied from slider I6 to the upper terminal of the primary winding of transformer I5 Yand the difference potential which is applied from the secondary winding of transformer I5 to the grid of tube'20 and amplified by such tube becomes applied as an amplified potential of phase .qbgupon the controlgrid of tube 30. However, since at the same time potential of phase @I is applied to the anode of tube 30, such tube will not fire and relays 3| and 2-3 will remain unoperated whereby the motor FVM will remain under the control of the R. P. M. motor unit 8 which simulates the speed of the No. 2 engine,

In a similar manner the No. 2 comparison circuit compares Vthe simulated engine speeds of the Nosl and 4 .engi-nes and controls the operation of switching relay |-4 to switch the aft vibrator motor AVM to the control of the R. P. M. motor unitsfG or I dependent upon which motor unit has been adjusted to simulate the greater engine speed.

What is claimed is:

1. Ina-ground trainer for simulating a multiengined aircraft, lmeans for simulating the engine and propeller vibrations, means operable representative of the speed of each of two engines, said vibration simulating means being associable with either of said latter means whereby it is operable at a speed commensurate with the engine speed represented by the operated means at the time associated therewith, means for comparing the represented engine speeds, and means controlled by said comparing means for transferring said vibration simulating means from one to the other of said speed representing means when the engine speed represented by the means at the time in control of the vibration simulating means is less than the speed represented by the speed representing means not in control speed.

2. In a ground trainer for simulating a multiengined aircraft, a motor, an eccentrically mounted weight driven thereby for simulating the engine and propeller vibrations, means operable representative of the speed of each of two engines, said motor being associable with either of said latter means whereby it is operable at a speed commensurate with the engine speed represented by the operated means at the time associated therewith, means for comparing the represented engine speeds, and means controlled by said comparing means for transferring said motor from one to the other of said speed representing means when the engine speed represented by the means at the time in control of the vibration simulating means is less than the speed represented by the speed representing means not in control.

3. In a ground trainer for simulating a multiengined aircraft, a motor, an eccentrically mounted weight driven thereby for simulating the engine and propeller vibrations, means operable representative of the speed of each of two engines, said motor being associable with either of said latter means whereby it is operable at a speed commensurate with the engine speed represented by the operated means at the time associated therewith, means for comparing the simulated speeds of said simulated engines, and a switching relay controlled by said comparing means for transferring said motor from one to the other of said speed representing means when the engine speed represented by the means at the time in control of the vibration simulating means is less than the speed represented by the speed representing means not in control.

4. In a ground trainer for simulating a multiengined aircraft, a motor, an eccentrically mounted weight driven thereby for simulating the engine and propeller vibrations, means operable representative of the speed of each of two engines, said motor being associable with either of said latter means whereby it is operable at a speed commensurate with the engine speed represented by the operated means at the time associated therewith, an electric power supply, means in said speed representing means for deriving potentials from said power supply which vary in accordance with the represented engine speeds, means for comparing said potentials, and means effective when potential derived in accordance with the engine speed representing means which at the time has control of said motor is less than the potential derived in accordance with the engine speed representing means which does not have control of said motor for transferring the control of said motor to said latter means.

5. In a ground trainer for simulating a multiengined aircraft, a motor, an eccentrically mounted weight driven thereby for simulating the engine and propeller vibrations, means operable representative of the speed of each of two engines, an electric power supply, means in each of said latter means for deriving a potential from' said power supply commensurate with the engine speed represented by the operated means at the time associated therewith, means for associating said motor with either of said latter means whereby it is operable at a speed commensurate with the represented engine speed, other means in each of said engine speed representing means for deriving a potential from said power supply commensurate with the engine speed, means for comparing said latter potentials, and means effective when potential derived in accordance with the engine speed representing means which at the time has control of said motor is less than the potential derived in accordance with the engine speed representing means which does not have control of said motor for transferring the control of said motor to said latter means.

6. In a ground trainer for simulating a multiengined aircraft, a motor, an eccentrically mounted weight driven thereby for simulating the engine and propeller vibrations, means operable representative of the speed of each of two engines, said motor being associable with either of said latter means whereby it is operable at a speed commensurate with the engine speed represented by the operated means at the time associated therewith, an electric power supply, means in said latter .means for deriving potentials from said power supply which vary in accordance with the represented engine speeds, an amplifier tube for amplifying the potential difference between said derived potentials, an electronic device responsive to the amplified difference potentials, and a switching relay controlled by said electronic device for transferring the control of said motor to the engine speed representing means which is at the time deriving a potential representative of a greater engine speed.

7. In a ground trainer for simulating a multiengined aircraft, a motor, an eccentrically mounted weight driven thereby for simulating the engine and propeller vibrations, means operable representative of the speed of each of two engines, means for normally associating said moto-r with one of said latter means whereby it is operable at a speed commensurate with the engine speed represented by the associated operated means, an electric power supply, means in said latter means for deriving potentials from said power supply which vary in accordance with the represented engine speeds of rotation, an amplifier tube for amplifying the potential difference between said derived potentials, a gas-filled tube responsive to said amplified potential only when said amplified potential signies that the engine speed of the engine speed representing means with which said motor is normally associated becomes less than the engine speed of the other engine speed representing means, and means responsive to the nring of said gas-filled tube to transfer said motor to the other engine speed representing means.

JOSEPH J. LUKACS.

No references cited. 

